Our research is directed at analysing the role of neurotransmitter receptors and ionic channels at particular synaptic sites in the vertebrate retina. Intracellular electrophysiology, in combination with drug application and single cell staining procedures, will be utilized to study retinal circuitry. The physiological roles of glutamate and GABA receptors in the distal retina and glycine receptors in the proximal retina will be explored. Experiments will be directed at demonstrating that receptor subtypes mediate particular visual pathways in the retina. The specific aims are to 1) distinguish and characterize the glutamate receptors on OFF bipolar and horizontal cells, 2) correlate glutamate receptor subtypes with particular ionic conductances, 3) evaluate the role of GABA receptors in mediating horizontal cell feedback, 4) describe the effects of light driven modulation of extracellular potassium concentrations on horizontal cell coupling, and 5) characterize glycine receptors and determine if other endogenous amino acids normally activate these receptors. The long term objective of this research is to employ pharmacological techniques as a tool to provide a description of the synaptic physiology of the retina. This information could provide a methodology for analysing visual information processing and for localizing sites of pathophysiology, particularly as it relates to retinal disease.